Since the diffusion of boron impurity atoms into silicon is necessary for semiconductor device fabrication, a number of boron containing chemicals and processes to "dope" the boron into the silicon have been proposed. Some of the known prior art products (and processes) are the following:
(1) boron nitride wafers are oxidized in a diffusion furnace to B.sub.2 O.sub.3 or HBO.sub.2, and the oxide is transferred in the vapor phase to the silicon wafer surface or boric oxide wafers can be used directly;
(2) boron tribromide liquid is vaporized and oxidized in the diffusion furnace to B.sub.2 O.sub.3 which coats the wafers from the vapor phase;
(3) boron trichloride is used as a source of boron ions for use with an ion implanter.
Less commonly used sources of boron include the boron spin-on solutions, (which typically are B.sub.2 O.sub.3 or a borosilicate glass precursor dissolved in a solvent) borosilicate films deposited by chemical vapor deposition, or diborane (B.sub.2 H.sub.6) gas, which is used in a procedure similar to that used for BBr.sub.3.
While the above are effective boron sources, all have disadvantages. Specifically, ion implantation involves high capital costs, low throughput, and damage to the silicon crystal structure, while boron oxide and related sources involve costly and complicated processes to achieve quality doping and/or create damaged or stained silicon surface.
Although spin-on boron sources offer the advantages of simpler processing, high throughput, and good uniformity of doping across the substrate, the currently available spin-on products suffer from the drawbacks of short shelf-life and high sensitivity toward ambient moisture.
It is thus apparent that a need exists for a spin-on boran dopant system that has a long shelf-life and whose processing and doping performance are not affected by ambient moisture.